First
>of all any surgeon
>who issues ironclad guarantees regarding results, strikes me as  terribly
>overconfident, perhaps even arrogant>

I will have to echo Susan's sentiments here.  Nothing but nothing is ever
guaranteed.  With this attitude, if the surgery doesn't produced the
"promised" results the doc most likely will blame you for not doing enough
this or that.
Do your own research or even get a second opinion.  As parents  of CP kids
we want so much to cure them.  At this point in time there is no cure for
CP.  Find out as much information, pro and con on the surgery and then make
your decision.  Surgery's can improve the life of a person with CP, bring
physical comfort etc but it still will require a life time commitment to
stretching etc.
Joanne